Webbing guide

ABSTRACT

A webbing guide for a vehicle safety comprises a guide surface in the form of a generally cylindrical bar ( 6 ) which has a continuous outer surface over which seat belt webbing passes in use following an upside-down U-shaped path. The surface comprises a top portion and two side portions ( 8 ) on either side of the top portion, and the top portion and at least one of the side portions are shaped so as to present a countered surface to the seat belt webbing. Preferably, the central area ( 7 ) of the top portion is raised, and the central area ( 9 ) of one or both side portions ( 8 ), is recessed, but the opposite contour arrangement could be provided with the central area of the top portion recessed and the central area of one or both side portions raised.

BACKGROUND OF THE INVENTION

The present invention relates to a webbing guide for a vehicle safetyrestraint seat belt. Such a webbing guide is Commonly known as a D-ringand is fixed to a vehicle support pillar behind the seat, approximatelyat shoulder level, to provide an upper anchorage for, and to guide, thebelt webbing as it changes direction from the vertical line coming fromthe retractor usually fixed at the base of the pillar, to a diagonalline across the occupant's torso.

Traditional webbing guides comprise a guiding surface in the form of abar suspended below a hole about which the guide is pivoted on thepillar. Ideally the bar should be set a large distance from the pivotpoint but this is impractical in the small space available in a vehicleand would make the guides too expensive for practical use.

A common problem with such guides is that the webbing tends to bunch atone end of the bar when it is subject to off-centre loads during acrash, increasing frictional forces between the webbing and the bar andinhibiting the free running of the webbing, leading to excess wear onthe belt, and additional crash loading for the vehicle occupant. Inextreme cases, the webbing can jam. This is evidently undesirable.Attempts have been made to minimise the problem for example by providinggrooves in the surface of the bar. This is expensive and has only shownlimited success in alleviating the problem.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved webbing guide.

A seat belt webbing guide comprising a guide surface in the form of agenerally cylindrical bar which has a continuous outer surface overwhich seat belt webbing passes in use, following an upside-down U-shapedpath, there being a top portion to the surface and two side portions,the top portion and at least one side portion are shaped so as topresent a contoured surface to the seat belt webbing.

Preferably, the central area of the top portion is raised, and thecentral area of the at least one of the side portions is recessed.

Alternatively, an opposite contour arrangement could be provided in thatthe central area of the top portion is recessed and the central area ofthe at least one side portion may then be raised.

The surface presented to the seat belt webbing may be smooth or may beprovided with formations such as being inset with grooves.

Preferably the contour of the surface is such that each warp and weftfibre of the belt webbing contacts the surface for a substantiallyidentical distance, i.e. the surface of the bar presented to thewebbing, has a substantially identical sized contour, measured in acircumferential sense around the bar, across the width and along thelength of the contact patch of the webbing with the loop.

According to a preferred embodiment of the present invention, each sideportion of the surface has its central area recessed.

The raised hump in the central area of the top portion of the surfaceeffectively vectorises the contact forces between the webbing and thesurface towards the centre of the surface, providing self-centring forthe guide. Additionally the transverse force components thus createdaugment frictional resistance to sideways movement of the webbing.

The guide of the invention thus has increased resistance to transversemovement of the webbing, thus resisting bunching of the webbing, andalso a self-centring property leading to improved stability.

The recessed side portion or portions serve to equalise the contactlength of the webbing with the guide over the width of the webbing toavoid higher loads in the centre which would cause excessive wear on thebelt and on the guide and possibly lead to failure.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how thesame may be carried into effect, reference will now be made to theaccompanying drawings in which:

FIG. 1 is an oblique side view of a guide according to the inventionwith contour lines marked to illustrate the unique shape of its surface;

FIG. 2 is an oblique bottom view of the guide of FIG. 1;

FIG. 3 is a side view of the guide of FIG. 1 illustrating the vectorisedload components.

FIG. 4 shows a length of seat belt webbing positioned about a web guide.

FIG. 5 shows an alternate embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The guide 1 has a mounting hole 2 through which a bolt is inserted tofix it to a vehicle support pillar. The mounting is done so that theguide 1 can pivot about this hole 2. A generally horizontal slot 3 isformed below the hole 2. This slot has up-turned ends 4. Belt webbing 5(see FIG. 4) passes through his slot in the vehicle, contacting theguide surface formed by the upper part of the generally cylindrical bar6, below slot 3. Arrow 20 shows the direction of travel of the webbing 5as the webbing moves out or the guide 1.

Preferably the contour of the surface is such that each warp 5 a andweft 5 b fibre of the belt webbing contacts the surface for asubstantially identical distance, i.e. the surface of the bar presentedto the webbing has a substantially identical sized contour, measured ina circumferential sense around the bar, across the width and along thelength of the contact patch of the webbing with the loop.

The central top area of bar 6 is raised with a smoothly contoured hump7. The side surfaces 8 of bar 6 have recessed, or depressed centralareas 9 (best seen in FIG. 2).

FIG. 3 illustrates the lines of forces on the bar 6 when webbing (notshown) is loaded.

The lines of force, shown by the arrows 10, 11, 12 are generallyperpendicular to the surface at any one point.

In the region of the apex of the central top hump 7, the lines of forceare therefore directed vertically along the centre line of the guide 1as shown by arrow 10. On each side of this arrow 10 are shown thevectorised loads to the sides of slot 3, and these are indicated byarrows 11 and 12. It can clearly be seen that these vectorised loadshave transverse load components, all directed inwards towards the centreline 10. Thus the guide 1 is self-centring with this shape ofconstruction.

Reference is made to FIG. 5, which illustrates an alternate embodimentof the invention in which the guide 1 includes a plurality of grooves 22on the guide surface.

What is claimed is:
 1. A seat belt system including a webbing guide andseat belt webbing comprising: a generally cylindrical bar having acontinuous outer guide surface over which the seat belt webbing passesin use, the outer guide surface having, in consecutive order in relationto a direction of travel of the webbing: a first or back side portion, atop portion, and a second or front side portion; wherein the outer guidesurface has a central region and two outer regions separated by andadjacent to the central region and the outer guide surface includes afirst contour, as viewed perpendicular to the direction of travel of thewebbing, the first contour being situated in a central region of the topportion, and a second contour, opposite to the first contour as viewedperpendicular to the direction of travel of the webbing, the secondcontour being in the central region of the first or back side portion ofthe bar, wherein one of the first and the other contour comprises araised portion, and the second contour comprises a recessed portion,such that each fibre of the belt webbing contact the outer guide surfaceof the bar for a substantially identical distance measured in acircumferential sense around the bar.
 2. An apparatus according to claim1 wherein the first contour is raised, and at least the second contouris recessed.
 3. An apparatus according to claim 1 wherein the outerguide surface is smooth.
 4. An apparatus according to claim 1 whereinthe shape of the guide surface effectively vectorises the contact forcesbetween the webbing and the surface towards a central area of thesurface, providing self-centering for the webbing.
 5. An apparatusaccording to claim 1 wherein the shape of the surface is such thattransverse force components created augment frictional resistance tosideways movement of the webbing.